The phenomenon of mate copying occurs when an individual female (observer) indicates a romantic preference for a partnered male (target) over an unpartnered male. To put it bluntly: The woman likes the taken guy more than the single guy. Mate copying has been documented countless times among non-human animals, but the body of empirical data confirming its existence in humans is rapidly growing.

While there have been observations of mate copying among both males and females, there is a strong theoretical reason for believing it occurs more frequently among females. Specifically, it solves a more important adaptive problem for females than for males—getting information about a potential partner. Because men are often initially concerned with the attractiveness of a partner, they can look at a female and instantly discern a fair bit of mate-relevant information. That's often less the case for women.

Think of mate copying as the real-life equivalent of LinkedIn’s endorsement feature: By being seen as John’s partner, Amanda (his girlfriend) is implicitly endorsing him for the skill of being a competent romantic partner. This information is pretty valuable, especially to some other women. It also turns out that this endorsement carries more weight depending on your own mate-relevant profile. In other words, how desirable you are as a mate helps to determine how desirable your partner is as a mate.

There are a few principles at work here. The first is the idea that humans generally employ a mating strategy of positive assortment. This is another way of saying that “like attracts like," or, to be more specific, individual similarity on a given dimension may predict association. Studies have demonstrated that people choose others with similar education levels, age, race etc. (one study even found that people tend to marry others with similar DNA). In this case, we can say that romantically desirable people generally partner with other romantically desirable people. This makes sense: I’m sure you can think of examples of romantic partnerships where one seems to be more desirable (to the opposite sex) than the other, but you can probably think of more in which each partner is comparably desirable. Think about attractive, wealthy, high profile celebrities—they often date other attractive, wealthy, high profile celebrities.

What does this have to do with mate copying?

The social currency afforded to you by being attractive is well known. People perceived as physically attractive have a number of advantages over others, including:

These are just a few. Attractive people have also been shown to outscore unattractive people on the dimensions of social desirability, presumed occupational status, social and professional happiness, and the likelihood that the person would marry in the future.

But it doesn’t end there. It’s good to be attractive, but what if you’re not? One thing you can do is get an attractive partner, or at least hang out with physically attractive people. Back in the 1970s, a pair of researchers conducted an experiment to examine the importance of having a physically attractive partner. Participants evaluated men who were either the boyfriend of, or unassociated with, a female; and the female was either attractive, or unattractive. Of the four conditions, the men with an attractive girlfriend were evaluated the most favorably. The men with the unattractive girlfriend were evaluated the least favorably. This was taken as evidence of how the company you keep seems to be important.

Scientific research on mate copying indicated that having a partner increases our desirability to the opposite sex, but almost all males will romantically pair (align) with a female at some point in their life. The [mate] quality of one’s romantic partner is more important than whether or not they have one.

Because physical attractiveness is an important cue for female mate-value, the perceived quality of a man’s female partner can be determined to a large extent by how physically attractive she is. Due to positive assortative mating, this can have a bearing on a man’s own mate-value. Some studies have demonstrated that mate copying effects are stronger when the female partner of a man is physically attractive than if she is less attractive or perceived as unattractive. In some research I personally conducted, a man’s mate-value was elevated simply by having physically attractive female friends.

It’s not all about looks, though: A study conducted in the UK found that in addition to physical attractiveness, mate copying may also be driven by character attractiveness. In the study, mate copying only occurred when the model female was smiling at the target male. Another study found that mate copying was only present when the female observer perceived romantic interest directed toward the male target by the female model. Taken together, these results suggest that the attractiveness of one’s female partner may be of critical importance in determining how likely mate copying is to occur.

Based on the research presented above, a man looking to romantically attract women might do well to surround himself with beautiful women. And if one (or all) of them behaves favorably toward him, all the better.

Mate copying is a noticeably unscrupulous way of seeking a partner. You also offered that it is done primarily by women. Do you think this has social sanctions? It is always pretty obvious to observe when attraction occurs. Would you say that society has accepted this as a form of mating rituals?
I also have noticed men of less social polish actually flagrantly advertising their promiscuity and cheating behavior in order to attract like-minded behavior. Is this becoming a popular trend?

My personal view on it is that mate-copying is atrocious. However, would I be wrong in assuming anyone who mate copies is unworthy of my loyalty, time or hard work?

You have to be careful not to confuse mate copying with mate poaching. Copying is really just expressing an admiration, whereas poaching involves attempting to pry an individual away from another.

Studies suggest that men also mate copy, but it is generally more prevalent among females. For both sexes there are strong moral and social proscriptions against poaching (taking that which is not yours). People generally understand this.

It is known that while some experience with the opposite sex is desirable in a mate, too much is a turn-off for most people. Few people are impressed by a potential mate boasting that he or she is very promiscuous. This type of promotion will attract a certain type of individual.